1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
As discussed above, a lithographic apparatus uses a patterning device to pattern incoming light. A static patterning device can include reticles or masks. A dynamic patterning device can include an array of individually controllable elements that generate a pattern through receipt of analog or digital signals.
Multiple layers can be formed on each substrate, with each layer receiving feature patterns that interconnect within that layer and to other feature patterns in previous/subsequent layers. However, typically only an alignment patterned formed on a top layer of the substrate is used to determine proper alignment of feature patterns with respect to each other. With tolerances getting smaller, it would be desirable for alignment of subsequent feature patterns to utilize alignment patterns on the top layer and one or more previously formed layers.
Therefore, what is needed is a system and method that allow for measurement or detection of alignment patterns on a top layer and one or more previously formed layers before forming a next feature pattern.